Efficient assembly processes for micro devices have not been developed, partially because, at the micro-scale, structures are fragile and easily breakable. Typically breakage at the micro-Newton force range cannot be reliably measured by most existing force sensors. So far the most straightforward and flexible operation methods run in an open loop format using a microprobe to physically manipulate the micro device. This method can be inherently risky without an on-line safety micro force regulation. As a result, this approach decreases overall yield and drives up the cost of micro devices. For these reasons, research into automating the micromanipulation processes have focused on micro force sensing and related control techniques.
In micro force sensing, cantilever beams are the most frequently implemented sensor structure type depending on its highly sensitive factor, and either static or dynamic operation mode. However, cantilever-based sensors introduce significant limitations for micro-force measurements during micromanipulation. First, the cantilever-based sensors have a relatively flexible structure which causes inherent difficulties with accurate manipulation of micro devices. Second, such sensors exhibit only a small dynamic range for maintaining high accuracy. To overcome these limitations, the present invention proposes an innovative active micro-force sensor based on the bilateral mechanical-electrical behaviors of piezoelectric films.